1. Field of the Invention
The present invention generally relates to an image formation device. More specifically, the present invention relates to an image formation device having a paper feed mechanism.
2. Background Information
A conventional image formation device includes an image formation unit and a paper feed mechanism. The image formation unit has a thermal head. With the conventional image formation device, an ink ribbon coated with a sublimation dye is laid over recording paper (printer paper). Electrical energy corresponding to image information is applied to the thermal head. Thermal energy generated by the thermal head sublimates the sublimation dye coating of the ink ribbon and transfers the sublimation dye onto the recording paper to perform specific printing, such as color printing. With the conventional image formation device, rendering of images having gradation is performed by controlling amounts of current sent to the thermal head, that is, amounts of heat generated by the thermal head.
The paper feed mechanism includes a feed roller and a press roller. The feed roller is rotationally driven. The press roller follows the feed roller. The paper feed mechanism is used to securely send the recording paper to the image formation unit a number of times (for example, three or four times). The feed roller and the press roller are usually constituted by a metal shaft. In particular, when the surface of the feed roller is made of metal, grip portions are formed on the feed roller by knurling (texturing in a reticulated pattern) so that the recording paper will be fed more reliably. The grip portions protrude beyond the other surface of the feed roller. The grip portions are prevented from touching the press roller. Also, a paper feed path, which is a gap through which the recording paper passes, is ensured between the feed roller and the press roller.
With another conventional image formation device, a gap ensuring member is further provided at a location a specific distance away from ends of the press roller to ensure the paper feed path (see Japanese Laid-Open Patent Application No. 2006-103864, for example). The gap ensuring member includes a gap roll. The press roller is biased toward the feed roller by a spring or other such biasing member.
With the conventional image formation device, biasing force of the biasing member bends the press roller at both ends toward the feed roller with the gap ensuring member as the fulcrum. As a result, a middle of the press roller bends away from the feed roller, which widens the gap between the press roller and the feed roller. Therefore, the press roller does not sufficiently press the recording paper against the feed roller. Also, the recording paper is not conveyed reliably.
With another conventional image formation device, the press roller further includes a middle portion and end portions to convey the recording paper reliably (see Japanese Laid-Open Patent Application No. 2005-324402, for example). The middle portion has a smaller diameter than the end portions. The end portions are integrally formed at both ends of the middle portion.
With the conventional image formation device, the middle portion is formed by cutting. Since the middle portion is considerably longer than the end portions, the cutting takes a long time. Also, a sliding material composed of a synthetic resin, for example, must be interposed between the press roller and a biasing member so that the press roller may follow smoothly. As a result, the number of parts and the cost of the image formation device are increased.
Another conventional image formation device further includes thermal roller bearings and press roller bearings to convey the recording paper reliably (see Japanese Laid-Open Patent Application No. H8-30137, for example). The thermal roller bearings are coaxially disposed at ends of a thermal roller and support the thermal roller at both ends of the thermal roller. The thermal roller bearings have a conical shape. A smaller diameter end of each of the thermal roller bearings is contiguous with the thermal roller. The press roller bearings are coaxially disposed at ends of a press roller and support the press roller at both ends of the press roller. The press roller bearings have a conical shape. A larger diameter end of each of the press roller bearings faces the press roller. Outer peripheral faces of the thermal roller bearings are pressed against outer peripheral faces of the press roller bearings to limit a gap between the thermal roller and the press roller.
With the conventional image formation device, the roller bearings have a complicated structure. Therefore, the number of parts and the number of assembly time are increased. As a result, the cost of the image formation device is increased.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved image formation device. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.